Devices and methods for “thermoanalysis” are known from the prior art and have now become established worldwide, in particular for purposes of material characterisation. Polymers, pharmaceutical substances, textiles, metals, ceramics and other organic or inorganic materials, for example, can thus be analysed and characterised.
In “thermoanalysis” (or “thermal analysis”), a sample to be investigated is subjected by means of a temperature regulating device (e.g. electrical heating device) to a controlled temperature change, e.g. a presettable “temperature program”. The sample may be heated, cooled or held at a constant temperature.
Complying as precisely as possible with the temperature program usually requires that the sample temperature is continuously detected, for example measured with a temperature measuring sensor, so that a detection or measurement signal representative of the sample temperature can be used for a control (e.g. PID control) of the sample temperature.
Moreover, during the controlled change in the sample temperature, at least one (further) signal characteristic of a (further) property of the sample is continuously detected and recorded together with the course of the sample temperature.
Thermoanalysis thus enables the investigation and characterisation of temperature-related changes in properties of a sample material, including processes triggered thermally in the sample.
It is understood that the term “continuously” used here in connection with a detection (e.g. measurement) of signals also includes a quasi-continuous detection, for example one taking place at relatively small time intervals (e.g. periodically).
Thermoanalytical methods can be specified more precisely depending on which further signal or which further signals (apart from the sample temperature) are detected during the controlled change in the sample temperature. Such special methods of thermoanalysis are also known from the prior art and do not therefore require further explanation here. The following methods are mentioned solely by way of example: differential thermoanalysis (DTA), differential calorimetry (DSC) or dynamic differential calorimetry (DDK), thermogravimetry (TG) or thermogravimetric analysis (TGA) and thermomechanical analysis (TMA).
TG or a “simultaneous thermal analysis” (STA), i.e. a combination of TG and DSC or DDK, is often used for the characterisation of thermal vaporisation and decomposition effects. In a further development, apart from the detection of a loss of mass of the sample, an investigation of gases that are liberated by the sample can for example also take place. For the gas investigation, use can be made for example of Fourier transform infrared spectrometry (FTIR) or mass spectrometry (MS, for example using a quadrupole mass spectrometer).
These known methods certainly offer the possibility of analysing volatile sample components and decomposition products. However, these methods come up against their limitations in practice when, over the temporal course of the thermal analysis, several or even many different components or decomposition products are liberated and a “time- or temperature-resolved” gas analysis process that is as good as possible is intended to be obtained.
Of concern here is the fact that the investigation of gases with the known gas analysis devices, depending on their accuracy, is relatively time-consuming—measured against the time typically provided for the course of a thermoanalysis or with regard to the temperature change rates typically provided in a temperature program (in the region of approx. 1 K/min to 50 K/min).
A more accurate investigation of thermally triggered gas liberation processes, in particular a more accurate characterisation of the gas composition when many different gases are liberated simultaneously, has therefore failed hitherto.